Flashtube for mounting on a space vehicle



Sept. 9, 1969 F. SILEO FLASHTUBE FOR MOUNTING ON A SPACE VEHICLE Filed July 5. 1967 INVENTOR.

z; ATTORNEY United States Patent US. Cl. 313-318 2 Claims ABSTRACT OF THE DISCLOSURE A fiashtube able to withstand temperature, vibration and shock extremes such as those encountered on a space vehicle wherein a quartz glass envelope bulb terminating in legs of a borosilicate glass; the borosilicate glass legs are hermetically bonded to elongated electrode holders made of an alloy having a nominal composition of 29% nickel, 17% cobalt, 0.45% manganese and the balance iron. These electrode holders terminate in threads. No physical contact with the brittle transparent envelope other than that provided by the low stress borosilicate glass to nickel-cobalt-iron alloy seal is necessary to mount this fiashtube, thereby minimizing thermal stresses to insure reliable operation when exposed to the extreme environments typical of a space mission.

Brief description of the invention The present invention relates to fiashtubes and more particularly to flashtubes mounted on space vehicles and missiles.

It has been found useful to mount lights exposed to the outside on space vehicles for various purposes. Such lights can be used for signaling, tracking, guidance, and cont-rol'. The space environment however is a very hostile environment to such lights and particularly to flashtubes. In such an environment, temperatures may change from about 250 F. to +500 F. in a short space of time. Furthermore, shock mounting is.not always possible so that usually, the lights or beacons are hard mounted on the vehicle or missile. The type of lamps and flashtubes useful at ordinary ambient situations are not suggestive of what to use in a space environment.

Generally speaking, the present invention contemplates a fiashtube useful in extreme temperature ranges wherein the transparent bulb or envelope is made of helically shaped quartz terminating in a borosilicate glass hermetically bonded to special nickel-cobalt-iron alloy electrode holders.

The invention as well as other objects and advantages thereof will become more apparent from the following description when taken in conjunction with the accompanying drawings.

Brief description of the several views of the drawings FIG. 1 is a longitudinal partly cross-sectional view of a fiashtube mounted in a reflector on a space vehicle;

FIG. 2 is a longitudinal perspective side view of the fiashtube shown mounted in FIG. 1; and,

FIG. 3 presents a front view of the fiashtube of FIG. 2.

Detailed description Shown in FIG. 1 is a beacon assembly 11 contained in a housing 13 mounted on a space vehicle. The housing 13 holds a reflector 15 having a central aperture neck section 17 which will hold the fiashtube 19. The neck section 17 has a wall 21 for holding a mounting insulator 23 which is held by bolts 25 to the wall 21. The ceramic high voltage mounting insulator 23 is for securing the electrode holders 27 and 29 of the electrodes 31, 33.

The ends 25, 37 of the electrode holders 27, 29 are threaded so that the electrode holders 27, 29 can be held in place by appropriate nuts 39 and conical spring washer 41. Electrical connections are made by attaching wires to terminal lugs 43 which are clamped between the nuts 39. The electrodes 31, 33 penetrate the legs 45, 47 of fiashtube 19 which has a helical configuration. The helical portion 49 thereof terminating in a tipoff 51.

The fiashtube is filled with high purity gases such as, but not limited to, xenon, argon, neon and various mixtures thereof to a nominal pressure of 300 mm. Hg. absolute. The nominal operating voltage is 2500 volts and the energy input is up to 500 watt seconds per flash. The minimum light conversion efficiency should be 40 lumen seconds per Watt-second and ignition should be a series type with no ignition wires required. The nominal ignition voltage is 25,000 volts.

In constructing the transparent envelope, the top of the envelope including the helix and the upper portion of the legs are of quartz. The quartz is sealed to borosilicate glass towards the bottom of the envelope, by means of a low stress graded glass seal arrangement. The borosilicate glass is heavied up to .050 minimum thickness for maximum strength at the seal and the spacing between adjacent quartz surfaces is 1 mm. minimum.

The borosilicate glass useful for the purpose of the present invention can be for example a Corning 7052 borosilicate glass having the following properties:

Thermal-expansion coeli, C., 0 to 300 C.-- 46 l0' Viscosity data:

Since the flashtubes will be subjected to extreme changes in temperature, the electrode holder to which the envelope is sealed should be made of a nickel-colbalt-iron alloy having the same thermal expansion properties as the borosilicate glass. Such alloys are obtained under the trade name of Kovar (Westinghouse) and Fernico (General Electric). A typical such alloy has the following properties.

Compositionabout 29% nickel; about 17% cobalt; about 0.45% manganese and the balance being about 52% iron.

Melting point-Approximately 1450 C. Density0.302 lb. per cubic inch. Hardness, annealed (-Rockwell)- B82 Hardness, cold worked-B Electrical resistivity49 microhms (cm. (cm.)

Thermal conductivity at 30 C.0.0395 ca1./(cm.) (sec.)

Thermal conductivity at 300 C.0.0485 cal./(cm.)

(sec.) (C.)

Since this alloy has thermal expansion properties which are very close to those of the borosilicate glass, the alloy need not be machined to feather edges in the seal area as is required for other metals; a strong joint can thus be obtained. This alloy can readily be machined for glassto-alloy seals. The sealing surfaces should be free from marks or scratches which extend across the sealing surface.

The alloy sealing surfaces must be thoroughly clean and free from gas or gas-forming components. If the surface is not degassed before sealing to glass, gas bubbles will form at the glass-metal interface as the seal is made. These bubbles will impair the mechanical strength of the seal. The alloy is degassed by heating it in a furnace to a temperature of 1050 C. for a period of 20 minutes. Hydrogen which is bubbled through a water trap is fed into the furnace to maintain a hydrogen atmosphere. The metal is moved to a cooling section of the furnace and cooled to 300 C. before it is removed from the furnace. Degassed alloy should not be touched with the hands especially the surfaces which are to be used for the glass seal. Glass-to-alloy seals should preferably be made within three hours after the alloy is degassed.

The alloy must be oxidized before glass can be sealed to it. This alloy may be oxidized during the sealing operation by heating it to about 650 C. in the oxidizing portion of the burner flame, or, it may be pre-oxidized in a furnace. The degree of oxidization for good seals is difficult to determine and a procedure of obtaining a suitable state of oxidation is best gained by experience. Heavily oxidized alloy yields mechanically strong seals, but these seals are not vacuum-tight. Under-oxidized alloy yields hermetic seals which are mechanically weak.

If the alloy is oxidized in the burner flame, the glass is sealed to the alloy while the temperature of the alloy is still between 650 and 800 C. The glass is fused and attached to the metal. Since the seal is small, the glass and alloy, which is suitably mounted, can be worked by hand.

After sealing, the threads must be cleaned of all traces of oxidation. Thus, only the body of the electrode holder is oxidized. The electrodes are of tungsten, either pure or modified with the addition of low work function materials such as, but not limited to, thorium oxide and bariumcalcium aluminate. Each electrode is machined as one piece and copper brazed to the nickel-cobalt-iron holder in a hydrogen atmosphere oven.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be 5 within the purview and scope of the invention and appended claims.

I claim: 1. A fiashtube for mounting on a space vehicle capable of operating from about 250 F. temperatures to about 500 F., comprising in combination;

(a) a quartz helical envelope for holding an electrode therein;

(b) legs extending out of said helical envelope, said legs containing a low stress graded glass seal terminating in a borosilicate glass;

(c) elongated electrode holders for holding electrodes therein, said electrode holders being an alloy having about 29% nickel, about 17% cobalt, about 0.45% manganese and the balance substantially iron, said elongated electrode holders being hermetically bonded to said borosilicate glass legs at one end and terminating in threads at the other, the portion intermediate said ends being oxidized, said threaded end being free of oxidation, and, a tungsten electrode passing through said electrode.

2. A fiashtube as claimed in claim 1 including two tungsten electrodes brazed to the electrode holders.

References Cited UNITED STATES PATENTS FOREIGN PATENTS 11/1964 France.

JOHN W. HUCKERT, Primary Examiner ANDREW J. JAMES, Assistant Examiner US. Cl. X.R. 

